Wash-off cleanser compositions in which soap comprises 50% or more, preferably 75% or more, preferably 90% or more of the surfactant system are based on traditional fatty acid soaps (alkali metal or ammonium salts of C8-C24 fatty acids), and the soaps are beneficial for deposition of benefit agent oil which may be used in these compositions. The soap also provides “squeaky-clean” rinse preferred by many consumers.
Soap-based cleaners with high levels of benefit agents, however, can be physically unstable under storage. The benefit agents are typically dispersed as a separate phase within the formulation (e.g., as emulsion or dispersion of fine particles under about 100 microns), and may possess density higher (for most particles) or lower (for skin-enhancing oils) than the bulk phase. The high viscosity of soap-based body washes is typically due to suspension of liquid/solid crystal domains within the bulk. This phase space fills the system and helps provide creamy texture as well as to structure against phase separation.
Upon storage at high temperature, however, the crystal phase can melt to yield a lower viscosity micellar phase and the benefit agents tend to cream to the top (most oils) or sediment to the bottom (most particles). This is both esthetically unpleasing and can affect product performance (uneven dosing). The present invention circumvents the stability problem by requiring the simultaneous presence of several additives to increases the physical stability of a soap-based personal washing formulation at higher temperatures and to improve the deposition of conditioning and/or skin appearance enhancing agents.
Specifically, the invention requires 10% to 50% by weight of a fatty acid blend of C12-C18 fatty acids, where the degree of neutralization of the blend is between 70% and 90%. It further requires 10-40% defined co-solvents; water levels at or below 18%, preferably at or below 16%, more preferably at or below 10%; incorporation of 3-20% emollient or occlusive oil (e.g., polar oils or non-polar oils such as mineral oil or petrolatum); a skin appearance and/or optical enhancing agent (e.g., mica, talc or titanium oxide); wherein polar or non-polar oil and/or enhancing agents are modified to improve dispersibility and stability (e.g., via treatment with hydrophobic agent such as multivalent soap and/or other hydrophobic agents, such as hydrophobically modified cationic or hydrophobically modified non-ionic polymer). It is only through this unique combination of criticalities that applicants have surprisingly achieved high deposition compositions which are stable.
The following references are noted:
US 2004/0234565 A1 discloses a composition used to alter the color of skin. Pigment is dispersed in an oil phase which is in turn dispersed within an aqueous phase containing synthetic surfactant and stabilized by carboxylic acid polymers.
US 2004/0223929 A1 discusses the combination of a hydrophobically modified interference (platy) particle dispersed in a skin compatible oil which is itself emulsified within an aqueous cleansing phase containing synthetic surfactants.
US 2005/0100570 A1 claims a personal cleansing formulation consisting of an aqueous phase and a dispersed oil phase. The aqueous phase is based on anionic synthetic surfactants and displays a shear thinning rheology.
US 2006/0239953 A1 describes a rinseable personal care composition containing a dispersed moisturizing oil phase. This phase is structured by co-addition of a high modulus oil structurant such as petrolatum, microcrystalline wax, polyethylene, or polydecene.
US 2007/0207936 A1 recognizes that body washes based on rod-like or worm-like micelles with high levels of emollient oil are generally unstable towards storage at elevated temperature. Stability can be improved if the surfactant system can be formulated into a lamellar phase through the specific combination of a cationic guar gum, sodium trideceth sulfate, lauroamphoacetate, and salt. A very low shear rate must be maintained while mixing the formulation so as to keep the lamellar phase dispersed as spherulites.
U.S. Pat. No. 6,987,085 B2 describes a skin cleanser with 20-50% fatty acids and fatty acid salts with 10-30% of the fatty acids being of chain length C20-C24. The systems discussed are richer in fatty acids of chain length C16 and longer than they are in acids of chain length C15 or shorter. The degree of neutralization of the fatty acid is kept in the range 70-90% and glycols or glycol ethers are also present at levels of 5-25%. The water content of the invention can range from 20-70%.
US 2007/0213242 A1 specifies an oxyethylenated derivative of behenyl alcohol or behenic acid at a 1% level to improve the high temperature storage stability of soap-based foaming creams.
US 2007/0213243 A1 proposes to solve the poor high temperature storage stability of soap-based liquid cleansers by addition of 6-8% of an alkali-swellable, crosslinked acrylic emulsion polymer. The fatty acids and acrylic acids are first fully neutralized and then back-treated with citric acid to reduce the pH into the range 7.7-8.7, where superior storage stability is achieved.
US 2003/0078172 A1 discloses a skin cleanser which fits the category of a foaming cream—an opaque, viscous aqueous medium which is comprised of a mixture of fatty acid (soaps) or other surfactants and other additives. This invention combines a wax such as camauba wax or beeswax (at 1-10%) and a surfactant system which forms a paracrystalline phase of direct hexagonal or cubic texture when the ambient temperature increases above 30° C. The paracrystalline phase remains stable up to at least 45° C. and so improves the storage stability of the foaming cream. The surfactants employed are a mixture of water-soluble and water-insoluble agents, such as the potassium salts of lauric and myristic acids (soluble) and the potassium salts of palmitic and stearic acid (insoluble). The insoluble salts contribute to the formation of the normal hexagonal phase. The levels of these surfactants should total 40-60%, with 5-35% insoluble and 15-35% soluble materials. Solvents such as glycerol and/or polyethylene glycol PEG 8 can be present at 5 to 20%.
Finally, as noted in cross-reference, applicants are filing on same date, in addition to the application for deposition of skin appearance and/or optical enhancing agent (e.g., TiO2), one application directed to deposition of make-up agents (e.g., iron oxide) and one directed to deposition of antimicrobial agents.